Wireless charging at substantially uniform charge rate for different physical charge configurations

Abstract

A wireless charging system for a planar wireless accessory includes a receiving coil positioned within the planar wireless accessory and a transmitting coil positioned within a planar electronic device. The transmitting coil generates a magnetic flux that is received by the receiving coil to charge a battery of the planar wireless accessory when the planar wireless accessory is positioned relative to the planar electronic device according to a select charging configuration of multiple user-selectable charging configurations. The transmitting coil and the receiving coil are shaped and positioned to charge the battery at a substantially uniform rate at each different one of the multiple user-selectable charging configurations.

What is claimed is: 
     
       1. A wireless charging system comprising:
 a receiving coil positioned within a planar wireless accessory; and 
 a transmitting coil positioned within a planar electronic device that generates a magnetic flux received by the receiving coil to charge a battery of the planar wireless accessory when the planar wireless accessory is positioned relative to the planar electronic device according to a select charging configuration of multiple user-selectable charging configurations, the transmitting coil and the receiving coil being shaped and positioned to charge the battery at a substantially uniform rate across the multiple user-selectable charging configurations. 
 
     
     
       2. The wireless charging system of  claim 1 , wherein the planar electronic device and the planar wireless accessory mate at an edge defining a relative angle of separation between the planar electronic device and the planar wireless accessory and wherein the multiple user-selectable charging configurations correspond to different angles within a range of user-selectable angles for which wireless charging is supported. 
     
     
       3. The wireless charging system of  claim 2 , wherein the planar wireless accessory is wirelessly charged at the substantially uniform rate when the relative angle of separation is zero degrees and also when the relative angle of separation is within a predefined range of nominal use angles that are obtuse. 
     
     
       4. The wireless charging system of  claim 3 , wherein a distance between the transmitting coil and the receiving coil is greater when the relative angle of separation is zero degrees than when the relative angle of separation within the predefined range of nominal use angles. 
     
     
       5. The wireless charging system of  claim 4 , wherein the transmitting coil includes a flat portion, the flat portion of the transmitting coil facing a flat portion of the receiving coil when the relative angle of separation is zero and facing a rounded edge of the receiving coil when the relative angle of separation is within the predefined range of nominal use angles. 
     
     
       6. The wireless charging system of  claim 1 , wherein the transmitting coil has a rectangular cross section. 
     
     
       7. The wireless charging system of  claim 6 , wherein the receiving coil has a cross section that is of non-rectangular shape and includes at least one rounded edge portion. 
     
     
       8. The wireless charging system of  claim 7 , wherein a cross-section of the receiving coil has at least one flat edge portion. 
     
     
       9. The wireless charging system of  claim 7 , wherein the receiving coil is asymmetrical along a first axis and also asymmetrical along a second axis perpendicular to the first axis. 
     
     
       10. The wireless charging system of  claim 9 , wherein the asymmetry along the first axis and along the second axis contributes to capture of a magnetic field by the receiving coil that remains substantially uniform as distance is varied between the transmitting coil and the receiving coil in different configurations of the multiple user-selectable charging configurations. 
     
     
       11. The wireless charging system of  claim 1 , further comprising:
 a transmitting coil shield with an L-shaped cross-sectional profile; and 
 a receiving coil shield with an asymmetrical cross-sectional profile. 
 
     
     
       12. A method for wirelessly charging a battery, the method comprising:
 generating, at a transmitting coil positioned within a planar electronic device, a magnetic flux; and 
 receiving the generated magnetic flux by a receiving coil positioned within a planar wireless accessory, the transmitting coil and the receiving coil being shaped and positioned relative to one another so as to charge the battery at a substantially uniform rate across multiple user-selectable charging configurations of the planar electronic device relative to the planar wireless accessory. 
 
     
     
       13. The method of  claim 12 , wherein the planar electronic device and the planar wireless accessory mate at an edge defining a relative angle of separation between the planar electronic device and the planar wireless accessory and wherein the multiple user-selectable charging configurations correspond to different angles within a range of user-selectable angles for which wireless charging is supported. 
     
     
       14. The method of  claim 13 , wherein the planar wireless accessory is wirelessly charged at the substantially uniform rate when the relative angle of separation is zero degrees and also when the relative angle of separation is within a predefined range of nominal use angles that are obtuse. 
     
     
       15. The method of  claim 12 , wherein the transmitting coil has a rectangular cross section and the receiving coil has a cross section that is of non-rectangular shape, the receiving coil including at least one rounded edge portion. 
     
     
       16. The method of  claim 15 , wherein the cross section of the receiving coil has at least one flat edge portion. 
     
     
       17. A wireless charging system comprising:
 a receiving coil positioned within a planar wireless accessory; and 
 a transmitting coil positioned within a planar electronic device that includes a flat edge portion and a rounded portion, the transmitting coil and the receiving coil being shaped and positioned to inductively charge a battery of the planar wireless accessory at a substantially uniform rate at each of multiple user-selectable charging configurations of the planar electronic device relative to the planar wireless accessory, 
 the flat edge portion of the transmitting coil being most proximal to the receiving coil when the planar wireless accessory is positioned in a first one of the multiple user-selectable charging configurations and the rounded portion of the transmitting coil being most proximal to the receiving coil when the planar wireless accessory is positioned in a second one of the multiple user-selectable charging configurations. 
 
     
     
       18. The wireless charging system of  claim 17 , wherein a distance between the receiving coil and the transmitting coil is greater in the first one of multiple user-selectable charging configurations than in the second one of the multiple user-selectable charging configurations. 
     
     
       19. The wireless charging system of  claim 17 , wherein the planar electronic device and the planar wireless accessory mate at an edge defining a relative angle of separation between the planar electronic device and the planar wireless accessory and wherein the multiple user-selectable charging configurations correspond to different angles within a range of user-selectable angles for which wireless charging is supported. 
     
     
       20. The wireless charging system of  claim 19 , wherein the planar wireless accessory is wirelessly charged at the substantially uniform rate when the relative angle of separation is zero degrees and also when the relative angle of separation is within a predefined range of nominal use angles that are obtuse.